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Welding on a small air compressor tank . . .

04-17-2009, 02:08 PM

I have a smallish air compressor pump I rebuilt, and just picked up a tank (DeVilbis) that had a dead compressor on it. I need to weld an additional pad on the top of the tank to take my motor. Any special precautions needed for welding to a 150psi rated tank? I'm guessing 1/8" E6013 or E7018, since they don't dig much, and low amps, and short-spaced and/or back-stepped beads not more than a couple of inches long. Can I reduce any introduced stresses with a little pre-heat? A burst compressor-tank can knock a wall right out of your garage!

well if it was mine i would trash the 6013's if you have 7018's,you say you need to weld a pad on i would just drag me a nice bead around it...make sure your heat is right before you start & open a valve on the tank so it can breath,,,make sure >NO< undercut or you have a chance for problems...this is just what i have done in the past with excellent results...6013 is an alright rod BUT if you have 7018's why waste your time with 6013...

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I have welded on lots of them over the years and one is still in my basement and i use it daily. But that was before i knew the rules or codes on welding on pressure vessels and how they should be done right. Someday i am going to cut mine up so no one ever gets hurt after i pass off this earth because it has to be pushing 40 years old...Bob

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I think with some enginuity you should be able to construct a mount bracket that bolts to the existing motor mount & a band to support it somehow would be the way to go. I would back away from the weld idea. If you can post some pics it would give me a better way of describing how to make the mounting bracket.

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I have a smallish air compressor pump I rebuilt, and just picked up a tank (DeVilbis) that had a dead compressor on it. I need to weld an additional pad on the top of the tank to take my motor. Any special precautions needed for welding to a 150psi rated tank? I'm guessing 1/8" E6013 or E7018, since they don't dig much, and low amps, and short-spaced and/or back-stepped beads not more than a couple of inches long. Can I reduce any introduced stresses with a little pre-heat? A burst compressor-tank can knock a wall right out of your garage!

And big chunks of metal can go flying like a grenade.
We have a thread or two about this stuff somewhere. With pics!
If you are SMART you won't do it. Unless maybe you build a cage around it like they have for mounting split rim truck tires.

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One of the things that bothers me about this is the experience of having cut up an old rusty tank; dismayingly thinwall construction. Yet I also once was shown a tank repair done by a long-time owner of a compressor sales and repair shop. I forget now whether he said it was a crack or a hole in the side of that small tank, but he had done a pretty rough looking brazing job over the top of it. I declined to buy his tank, but his assurance that it was fine made me think that they must be less critical than I had assumed. Still, my inclination is to be conservative when I don't KNOW and can only guess.

I could ask you what steel is customarily used for these tanks, but that probably varies depending on whether the tank was built here or is constructed of Chinese mystery metal. One positive sign is that this tank feels considerably heavier than others I've lifted.

I mentioned E6013 only as an example of a rod that doesn't penetrate as much as some, and I personally haven't run any of it in decades. If I were to weld on this tank, I'd use E7018, 3/32" rather than 1/8". But since I don't know what I'm doing, Sundown, and since I haven't yet been told how to do it successfully, I suppose I won't.

The existing pad is awfully small for cantilevering much structure off one end to support a heavy weight. I guess what I could do is make a pad that I can strap to the tank with a couple of home-made band-clamps. Or just look for another tank.

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doing the strap thing would be just wrong...if you can weld then 7018 3/32 rod will work & if your scared then get someone that can weld to do it,no need in wasting this tank...IT CAN BE DONE & is done everyday...i told you how to do it....

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Just because it might be "done everyday" doesn't make it right and it sure as he11 doesn't make it safe.

The OP is getting some bad advice here. There's a reason why pressure vessels are certified.

Thunder, you seem to be one who likes to go against generally accepted industry standards (using pure tungsten in an inverter) and welding on pressure vessels without the proper credentials.

I'd like to be the lawyer representing the plantiff when one of your "out of the box" solutions blows up and injures or kills someone. I guarantee you don't have enough insurance to cover the potential damages.

I've seen some of your work and it's good. I don't understand your position on this issue. A dang $100 tank isn't worth someone getting hurt over. To recommend stick welding that tank without having a clue about the OP's "welding experience" is just flat out reckless.

If it was absolutely necessary to add a motor support to this existing tank, I'd fabricate a bracket with a saddle that fit over the circumference of the tank and braze the saddle in place. Lot less chance of changing the metalurgy of the existing tank.

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don't listen to me i'm just a dumbass without a clue....but with experiance & i do it almost everyday with the dynasty 350 use 100% green tungsten with good results but you know it all comes down to the operator of the machineyour right i don't know if this guy can weld or not he did not say...in my day i was boiler & pressure vessel certified & was qualified to use the "R" stamp without ever having any problems...............................

Just because it might be "done everyday" doesn't make it right and it sure as he11 doesn't make it safe.

The OP is getting some bad advice here. There's a reason why pressure vessels are certified.

Thunder, you seem to be one who likes to go against generally accepted industry standards (using pure tungsten in an inverter) and welding on pressure vessels without the proper credentials.

I'd like to be the lawyer representing the plantiff when one of your "out of the box" solutions blows up and injures or kills someone. I guarantee you don't have enough insurance to cover the potential damages.

I've seen some of your work and it's good. I don't understand your position on this issue. A dang $100 tank isn't worth someone getting hurt over. To recommend stick welding that tank without having a clue about the OP's "welding experience" is just flat out reckless.

If it was absolutely necessary to add a motor support to this existing tank, I'd fabricate a bracket with a saddle that fit over the circumference of the tank and braze the saddle in place. Lot less chance of changing the metalurgy of the existing tank.

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Wow! Things I did not know about welding pressure tanks this thread has been somewhat educational for me.

Although Iíve done a little bit of welding on a tank or two.
Hereís a pic of one of those tank I did little welding to after welding up all the holes I think it came out ok. LOL!

But in all fairness and a logical point I personally would just buy a tank that would give me enough room on the platform to accommodate the motor and pump. Safety should always come first!

Many years ago I watched my dad build his own compressor needless to say it did work for awhile but it did fracture on a couple of welds luckily no one got hurt as we all worked around or in the same vicinity, so all the work he went through seemed to me be more of a cost than just buying a new compressor for a few dollars more with no worries. Sheeeew that was 30 years ago.

Compressors can be bought cheap enough in todayís market usually just a few dollars more than the cost of the materials, consumables and labor it takes to modify and repair one.

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Don't modify the tank. Build a frame to hold the tank and the pump independently.

I'm going to guess that seattle smitty is in Washington state based on the name. Start with the rules: http://www.lni.wa.gov/TradesLicensin...Book012009.pdf Note the LEGAL requirements for doing repair on a pressure vessel (in the 296-104-500's), and note that there is exemption for unfired vessels less than 5cuFt (about 40 gal) (sec 70.79.080) A 40gal tank at 100PSI is one heck of an explosive device. There is a photo floating around (in the previously mentioned thread, I Think) of what a tank of about twice this size does to a locomotive when it lets go.

If there is a failure (probability low, but decidedly not zero), what is the penalty? (probably high) What will your insurance do if you make an alteration, though technically legal, and a failure occurs, even if what you do has nothing to do with the failure? If your insurance company finds out you do this, will they just cancel the policy (hint: it is quite possible. read the policy) retroactively (they can do this too, and then nail you for fraud.) These are things that have happened locally to me in the last year. My AI was involved in investigating a brutal one in a school (no injuries or fatalities, fortunately, since it happened at night) with about a 40gal tank for HVAC controls.

This is not something to play at. Failures don't happen often, but the price is high when they do. Kind of like with an oil refinery.